This invention relates to high molecular weight perfluorocyclobutane polymers and methods of polymerizing trifluorovinyl monomers to form such polymers in the presence of a catalyst or initiator.
A number of references disclose the thermal polymerization of trifluorovinyl-containing monomers, typically bis-trifluorovinyl monomers, to form perfluorocyclobutylene polymers, including U.S. Pat. Nos. 5,037,917, 5,159,038, 5,364,917, 5,066,746, 5,159,037, 5,023,380, 5,162,468, 5,037,919, 5,198,513, 5,021,602, 5,210,265, 5,037,918, 5,159,036, 5,246,782, 5,409,777, and 5,364,547, the teachings of which are incorporated herein by reference. Disclosed reaction conditions involve heating monomers to temperatures of typically about 150-210xc2x0 C. for several hours. The resulting polymers xe2x80x9cpreferably have a molecular weight of from about 300 to about 30,000.xe2x80x9d (U.S. Pat. No. 5,037,917 at col. 2, ln. 38).
U.S. Pat. Nos. 5,037,918 and 5,159,036 disclose the use of xe2x80x9ccrosslinking initiating meansxe2x80x9d on perfluorocyclobutane polymers, subsequent to a completed step of polymerization, to obtain crosslinked polymer gels. Such crosslinking is further described in co-owned U.S. Pat. No. 5,246,782, at col. 3 ln 48xe2x80x94col. 4, ln. 28 and at col. 11, lns. 11-31.
Briefly, the present invention provides high molecular weight perfluorocyclobutane polymers and methods of polymerizing trifluorovinyl containing monomers to form high molecular weight perfluorocyclobutane polymers in the presence of a catalyst or initiator.
In this document:
xe2x80x9cC(number)xe2x80x9d refers to a chemical moiety containing the indicated number of carbon atoms; and
xe2x80x9csubstitutedxe2x80x9d when used without reference to a particular substituent, means substituted by conventional substituents which do not interfere with the desired product or process, e.g., substituents can be alkyl, alkoxy, aryl, phenyl, halo (F, Cl, Br, I), cyano, nitro, etc.
The present invention provides high molecular weight perfluorocyclobutane polymers and methods of polymerizing trifluorovinyl containing monomers to form high molecular weight perfluorocyclobutane polymers in the presence of a catalyst or initiator.
Monomers useful in the method of the present invention contain two or more polymerizable trifluorovinyl groups. Monomers are preferably of the formula CF2xe2x95x90CFxe2x80x94Xxe2x80x94R1xe2x80x94Xxe2x80x94CFxe2x95x90CF2, where each xe2x80x94Xxe2x80x94 is independently selected from the group consisting of: xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94SOxe2x80x94, xe2x80x94SO2xe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94NHxe2x80x94, and xe2x80x94NR2xe2x80x94, wherein R2 is C1-C25 substituted unsubstituted, saturated or unsaturated alkyl or aryl and R1 is a substituted or unsubstituted C1-C30 aryl or alkyl moiety which may additionally comprise heteroatoms. Preferably X is oxygen. Preferably, R1 is a C1-C16 aryl or alkyl moiety. Suitable monomers disclosed in the background references cited above may be used. Mixtures of monomers may additionally be used. PCFB oligomers or lower molecular weight PFCB polymers can also be used in place of or along with monomers to produce higher molecular weight polymers according to the present invention. Monomers containing three or more polymerizable trifluorovinyl groups may be added to create branch points.
We have found that the use of initiators or catalysts can result in a higher molecular weight polymer. Preferred initiators or catalysts include salts comprising fluorine-containing anions, more preferably anions selected from Fxe2x88x92, BF4xe2x88x92, PF6xe2x88x92 and SbF6xe2x88x92, more preferably Fxe2x88x92 or PF6xe2x88x92 and most preferably PF6xe2x88x92. Useful initiators or catalysts include alkylammonium, alkylsulfonium or alkylphosphonium salts and salts of organometalic complex cations. Preferred initiators or catalysts include alkylammonium salts. Most-preferred initiators or catalysts include (alkyl)4N+PF6xe2x88x92, wherein the alkyl group is a C1-C8 alkyl group, including (CH3)4N+PF6xe2x88x92 and (n-C3H7)4N+PF6xe2x88x92 (available from Aldrich Chemical Co., Milwaukee, Wis.). Without wishing to be bound by theory, it is believed that preferred initiators or catalysts include fluoride generators.
Polymerization involves joining trifluorovinyl groups of different monomer molecules to form linking perfluorocyclobutylene (PFCB) groups. Any suitable reaction conditions and equipment may be used, including batch or continuous processes. Suitable conditions and equipment disclosed in the background references cited above may be used. In addition, the present method has the advantage of allowing the use of lower reaction temperatures.
In the present method, the initiator or catalyst is preferably added to the reaction mixture (comprising monomers, oligomers, or combinations thereof) prior to heating the reaction mixture to reaction temperature or after the reaction mixture reaches reaction temperature, during polymerization. The initiator or catalyst is preferably added to the reaction mixture before it reaches reaction temperature or more preferably before heating. Reaction temperature may be between 100 and 300xc2x0 C. but is more typically between 120 and 250xc2x0 C. and preferably 150-200xc2x0 C. Reaction time is typically 1-24 hours. Solvent may be added. Addition of solvent may improve the activity of the initiator or catalyst by solvating initiator or catalyst.
Crosslinkers or branching agents containing three or more reactive trifluorovinyl groups may be added. Exemplary agents include tris(trifluorovinyloxyaryl)alkanes such as 1,1,1-tris(4xe2x80x2-trifluorovinyloxyphenyl)ethane and others cited in U.S. Pat. Nos. 5,037,918 and 5,159,036, incorporated herein by reference. Preferably the polymer according to the present invention is not crosslinked after polymerization and no crosslinking step is carried out after polymerization.
The resulting polymers have typical weight average molecular weights of two to eight or more times higher than the same polymerization performed without added initiator or catalyst. For comparison, polymers made under typical conditions of about 200xc2x0 C. for about 72 hours demonstrate typical weight average molecular weights of about 60,000. Preferably polymers of the present invention (made without added crosslinking or branching agents) have a weight average molecular weight (Mw) of 100,000 or greater, more preferably 130,000 or greater, more preferably 160,000 or greater, and most preferably 190,000 or greater.
This invention is useful in the manufacture of high molecular weight PFCB polymers.
Objects and advantages of this invention are further illustrated by the following examples. The particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this invention.